OBJECTIVES: (a) To isolate and characterize the etiologic agents causing transmissible spongiform encephalopathies in animals (scrapie and transmissible mink encephalopathy) and humans (Creutzfeldt-Jakob Disease) using hamster-adapted models of disease and techniques such as polyacrylamide gel electrophoresis, linear log sucrose gradients, filtration, ion exchange chromatography, and selective degradation procedures; (b) Study the pathogenesis of the spongiform encephalopathies in suitable hosts; (c) Study the etiologic and epidemiologic interrelationships between the animal and human encephalopathies, and (d) To study mechanisms by which conventional viruses produce slow infections using Newcastle disease virus to infect chickens.